1. Field of the Invention
Apparatuses consistent with the present invention relate to a micro electro mechanical system (MEMS) device, and more particularly, to an MEMS device that performs precise scanning by structurally preventing deformation of a stage having a light reflecting surface and includes a precise sensing structure for detecting the rotation speed and direction of the stage.
2. Description of the Related Art
MEMS devices are frequently used in display devices, laser printers, precise measuring instruments, precise machining devices, etc. For example, in a display device, an MEMS device is used as an optical scanner for reflecting or deflecting a scanning light beam onto a screen.
A related art MEMS device includes a stage formed with a light reflecting surface, a driving coil wound around the light reflecting surface of the stage, and a magnet forming a magnetic field across the driving coil. During the operation of the MEMS device, the stage is rotated in a direction determined by the Lorentz law due to the interaction between a current applied to the driving coil and the magnetic field formed by the magnet, and thus light incident onto the light reflecting surface of the stage is reflected onto a screen in a predetermined scanning direction. Since the driving coil is wound around the light reflecting surface of the stage, the size and inertia mass of the driving coil increase, thereby decreasing the driving efficiency of the MEMS device. Furthermore, since the driving coil is wound around a relatively large area, the magnetic field should travel a relatively long distance. This lowers the strength of the magnetic field and causes a driving power loss.
To address these problems, the light reflecting surface is formed on a top surface of the stage, and the driving coil is formed on a bottom surface of the stage within an inner region of the light reflecting surface. However, in this case, the light reflecting surface directly receives heat generated from the lower driving coil and thus undergoes thermal deformation. Therefore, incident light is not precisely reflected from the light reflecting surface of the stage in a desired scanning direction. For this reason, there is a need for an improved structure that can increase the efficiency of the MEMS device and keep the stage flat.
Meanwhile, to realize a high-resolution display device, an optical scanner should scan a screen very precisely. For this, there is a need for a sensor that can precisely detect the rotation of a reflecting mirror of the optical scanner.